This section provides background information to facilitate a better understanding of the various aspects of the invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Oil is known to progress to natural gas in deep sedimentary basins. A conventional view of oil-to-gas conversion is that oil thermally cracks to gas (thermal gas) at temperatures between 150° C. and 200° C. Temperatures in this range are commonly observed geologically where most oil-to-gas is observed. However, various kinetic models based on thermal gas have had only marginal predictive success in drilling operations. There is mounting scientific evidence suggesting that oil should not crack to gas, even over geologic time periods, at temperatures between 150° C. and 200° C., the range within which most so-called thermal gas is formed. For example, gas produced by industrial thermal cracking of hydrocarbons is typically severely depleted in methane and does not resemble the natural gas distributed in the earth.
The inventor of the present invention has previously disclosed that sedimentary rocks (e.g., geological formations) possess natural or intrinsic catalytic activity that generates natural gas (e.g., catalytically generated gas) in subterranean environments from heavy hydrocarbons. The inventor has disclosed methods for promoting (e.g., enhancing) the natural catalytic generation of light hydrocarbons in subterranean formations and in surface reactor systems, for example in WO2007/082179, U.S. Pat. No. 7,845,414, US 2011/0077445, and US 2010/0200234, all of which are incorporated herein by reference. Carbonaceous sedimentary rocks (i.e., source rocks) include, for example, shales containing kerogens (siliceous and carbonate), coals, tar sands, and reservoir rocks containing residual oil. Non-carbonaceous sedimentary rocks include, for example, sandstones and carbonate rocks, which contain inorganic carbon. Both carbonaceous sedimentary rocks and non-carbonaceous sedimentary rocks may contain transition metals. According to aspects of these prior disclosures, the source rocks comprise heavy hydrocarbons and catalytic sites (e.g., transition metals) that react generating catalytic gas.
Catalytic conversion of hydrocarbons into natural gas mediated by transition metals is an explanation for geologic formation of gas. For example, crude oils can be catalytically converted to gas over zero-valent transition metals (ZVTM) such as, for example, Ni, Co, and Fe under anoxic conditions at moderate temperatures (150° C.-200° C.). The catalytically-formed gas is typically identical or substantially similar to geologically-formed gas. According to these various methods of generating catalytic gas in subterranean formations and in surface reactors, an anoxic stimulation gas is injected into the subterranean formation or through the source rock in the surface reactor. According to the prior teachings, the stimulation gas, which may be a hydrocarbon gas, is not a reactant in the catalytic gas generation process. The stimulation gas is only used as an agent to carry hydrocarbons in the source rock to the catalytic sites. In other words, the use of a hydrocarbon stimulation gases is no different from inert gases such as nitrogen, helium, and carbon dioxide. The stimulation gas injected into the subterranean formation, via a well, is recovered from the well in the same molecular form.
There is continuing desire to identify sources of hydrocarbons as an energy source. There is a still further desire to promote the production of oil and gas to increase the production life of wells.